The Sig Sauer MPX Gen II Caliber Exchange Kit (brand part number CALXMPX4B9G2) is a 4.5-inch 9mm Luger barrel built specifically for the Second Generation MPX platform. Made by Sig Sauer from black carbon steel, this factory replacement barrel lets existing MPX Gen II owners refresh or repair their pistol-length barrel with a genuine Sig-built part rather than an aftermarket guess. As a caliber exchange component, it is built to the exact tolerances of the Gen II receiver, unlike the original Gen I MPX barrels.

Key Specifications

• Chambered in 9mm Luger, the MPX platform’s primary caliber.
• Barrel length is 4.5 inches, matching the pistol-length MPX configuration.
• Constructed from black carbon steel for durability.
• Built specifically for the Second Generation MPX platform.
• Sold as a caliber exchange kit barrel component.

Frequently Asked Questions

Will this fit a Gen I MPX? No, this barrel is built to Second Generation MPX tolerances and is not interchangeable with Gen I parts.

Does buying a bare barrel involve any special paperwork? No, purchasing the barrel alone does not require NFA paperwork; note that pairing a sub-16-inch barrel with a shouldered rifle-configured MPX lower without an approved registration would create a Short-Barreled Rifle.

Buy the Sig Sauer MPX Gen II 4.5-inch Barrel

Refresh your Second Generation MPX with a genuine Sig-built barrel. Order this handgun barrel from our Lubbock, Texas gun shop, and we will get it to your door as soon as it’s ready to ship.